1. Field of the Invention
The present invention relates to a rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, a rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor having a tetradecahedral structure in particular, a process for preparing the phosphor, and a radiographic image conversion panel using the phosphor.
2. Description of the Related Art
As a method which can replace conventional radiography, a radiographic image recording and reproducing method using a stimulable phosphor is known as described, for example, in Japanese Patent Application Laid-Open (JP-A) No. 55-12,145. This method utilizes a radiographic image conversion panel containing the stimulable phosphor (cumulative phosphor sheet) This method comprises the steps of absorbing radiation, which has passed through a subject or been emitted from an object to be examined, into the stimulable phosphor of the panel, then exciting the stimulable phosphor in accordance with a time series by an electromagnetic wave (exciting light) such as visible light, infrared light, or the like to thereby allow the radiation energy accumulated in the stimulable phosphor to emerge as fluorescent emission (stimulable emission), obtaining an electric signal by photoelectrically reading the fluorescence, and subsequently reproducing the radiographic image of the subject or object to be examined as a visible image based on the electric signal obtained. The panel, after being read, is subjected to the erasure of the remaining images so as to be made ready for subsequent photographing. That is, the radiographic image conversion panel can be used repeatedly.
The above-described radiographic image recording and reproducing method provides an advantage that radiographic images having abundant information can be obtained by a radiation dosage far smaller than that in conventional radiography using a combination of a radiographic film and sensitized paper. In addition, whereas a radiographic film is consumed for each photographing operation in conventional radiography, the above-described radiographic image recording and reproducing method makes it possible to use the radiographic image conversion panel repeatedly, thereby providing advantages in terms of the aspects of resource protection and economic efficiency.
The stimulable phosphor is a phosphor which emits stimulable emission when irradiated with exciting light subsequent to irradiation with radiation. In practical terms, generally used is a phosphor which emits stimulable emission in a wavelength range of from 300 to 500 nm by an exciting light in a wavelength range of from 400 to 900 nm. Examples of the stimulable phosphor hitherto used in a radiographic image conversion panel may include a rare earth element-activated alkaline earth metal fluorohalide based phosphor. The basic structure of the radiographic image conversion panel for use in the radiographic image recording and reproducing method is composed of a support and a stimulable phosphor layer provided on the support. However, the support is not necessarily needed if the stimulable phosphor layer is a self-supporting layer. Normally, the stimulable phosphor layer is composed of a stimulable phosphor and a binder which contains and maintains the substance in a state of a dispersion. Further, there has been known a stimulable phosphor layer which does not contain a binder and is composed solely of a stimulable phosphor in a state of a flocculated body formed by vapor deposition or sintering thereof. Furthermore, there has been known a radiographic image conversion panel having a stimulable phosphor layer in which a polymeric substance is impregnated into the gaps in the flocculated body of a stimulable phosphor. Whichever type is selected from these stimulable phosphor layers, the stimulable phosphor emits stimulable emission when irradiated with an exciting light subsequent to irradiation with radiation such as X-rays. Therefore, the radiation transmitted through a subject or emitted from an object to be examined causes the energy in an amount proportionate to the amount of the radiation to be absorbed in the stimulable phosphor layer of the radiographic image conversion panel so that a radiographic image of the subject or the object to be examined is formed as an image of accumulated radiation energy in the panel. This accumulated image can be released as a stimulable emission by the irradiation of the exciting light. Consequently, the photoelectric reading of this stimulable emission and the conversion thereof into an electric signal make it possible to convert the accumulated radiation energy image into a visible image.
The surface of stimulable phosphor layer (i.e., the surface of the layer not facing the support) has normally a protective layer composed of a polymer film or a vapor-deposited film of an inorganic substance to thereby protect the stimulable phosphor layer from chemical deterioration or physical impact.
Since the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor has an excellent sensitivity and provides a radiographic reproduction image having a high level of sharpness when the substance is used as a radiographic image conversion panel, it can be a practically excellent stimulable phosphor. However, as the practical use of radiographic image recording and reproduction method has advanced, there has been a growing demand for further advances in the stimulable phosphor. Because of this demand, after the examination of the grain shape of the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphors hitherto utilized, the present inventors have found that these substances are made up of tabular grains. Conventionally known processes for the preparation of the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphors comprise the steps of dry-blending or blending by suspending in a water-based medium the material compounds, which are an alkaline earth metal fluoride, an alkaline earth metal halide other than fluoride, a halide of a rare earth element, ammonium fluoride, and so on, firing these compounds, after the addition of a sintering preventing agent if necessary, and pulverizing the fired product. Accordingly, since the pulverizing step after the firing step is substantially essential to the conventional processes, most of the grains of the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphors produced in the above-described manner were tabular (hereinafter referred to simply as xe2x80x9ctabular phosphorxe2x80x9d on occasion).
In a stimulable phosphor layer obtained by coating a mixture of the above-described tabular-grained phosphor and a binder resin solution on a support and drying the coating, the tabular-grained phosphor tends to be arranged such that the surface of the tabular-grained phosphor is parallel to the surface of the support, as illustrated in FIG. 1. If a radiographic image is stored in a radiographic image conversion panel having a stimulable phosphor layer, in which the tabular-grained phosphor is arranged in the above-described manner, and thereafter the panel is irradiated with an exciting light, the exciting light and the stimulable emission generated tend to extend in a transverse direction (i.e., a direction parallel to the surface of the support) (refer to the horizontal arrow in FIG. 1). This phenomenon presents a problem that the sharpness of radiographic reproduction images is liable to drop.
Based on the foregoing, in order to inhibit the drop in the sharpness of the radiographic reproduction images in the radiographic image recording and reproduction methods, an attempt to use a stimulable phosphor made up of approximately cubic grains has been proposed, as disclosed in JP-A No. 62-86,086. However, the reproducibility of the process for preparing the stimulable phosphor made up of approximately cubic grains disclosed above is not sufficient for industrial use.
Further, JP-A No. 7-233,368, Japanese Patent Application No. 6-315,673, and JP-A No. 10-195,431 disclose a process for preparing a rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor having a tetradecahedral grain structure in which grain shape and grain aspect ratio are controlled (hereinafter referred to simply as xe2x80x9ctabular phosphorxe2x80x9d on occasion). In a radiographic image conversion panel having a stimulable phosphor layer in which a rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor having a tetradecahedral grain structure (hereinafter referred to simply as xe2x80x9ctetradecahedron-structured phosphorxe2x80x9d on occasion) is provided, the polarity of the tetradecahedron-structured phosphor is so reduced, as illustrated in FIG. 2, that the undesirable transverse extension of the exciting light and the stimulable emission is lessened and therefore the sharpness of resultant radiographic reproduction images increases. Despite very high-level emission characteristics, sharpness in particular, of the phosphors obtained by the processes for preparation thereof disclosed in the above-mentioned publications, further improvement of sensitivity and erasure characteristics of the phosphors has been required of the phosphors for use in radiographic image recording and reproduction.
Furthermore, in the above-mentioned processes for preparing the phosphors, use is made of ammonium halide as a reactant mother liquor, to which an aqueous solution of a barium halide and an aqueous solution of an inorganic fluoride salt are simultaneously added so as to allow the reaction to proceed to there by synthesize stimulable phosphors. However, the grains produced by this procedure tend to have high aspect ratios. In contrast, although the aspect ratios can be brought somewhat closer to 1 if the barium halide is added to the reactant mother liquor in advance, this procedure is not satisfactory from the standpoint of controllability of grain shape, grain size, and grain size distribution.
Accordingly, it is an object of the present invention to provide a rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor capable of producing high-quality images having a very high sharpness and exhibiting other excellent emission characteristics, high sensitivity and erasure characteristics in particular, when used in radiographic image recording and reproduction, a process suited for the preparation of the phosphor, an apparatus for the preparation, and a radiographic image conversion panel using the phosphor.
Another object of the present invention is to provide a novel process for preparing a rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, which process is highly capable of controlling the grain shape, grain size, and grain size distribution of the grains of the stimulable phosphor. In particular, it is an object of the present invention to provide a novel process for preparing a rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor capable of providing high-quality images exhibiting a very high sharpness together with good sensitivity and granularity, when utilized in a radiographic image conversion panel, and a reaction apparatus in which the process is used.
In the aforesaid literature concerning phosphors, no mention is made of grain size and grain size distribution of the phosphors. However, for the improvement of image quality when a phosphor is used in a radiographic image conversion panel, the mere control of the grain shape and the grain aspect ratio of the phosphor to be used is not sufficient and it is desired to simultaneously control the grain size and grain size distribution. The present invention has been achieved by finding that the grain size and the grain size distribution are factors capable of significantly influencing the image quality when the phosphor is used in a radiographic image conversion panel and by finding proper ranges for the grain size and the grain size distribution.
The simultaneous control of the grain shape, grain aspect ratio, grain size, and grain size distribution is performed in a precipitation reaction of crystals of phosphor precursor wherein an aqueous solution of BaX2 (X is at least one halogen selected from the group consisting of Cl, Br, and I) is the reactant mother liquor. In this case, it is difficult to satisfy all of the required conditions for the grains at the same time by mere control of the concentration of BaX2 because the controllable range is narrow. Therefore, the present invention has been achieved based on the finding that the required conditions for the grains can be satisfied at the same time by a combination of control of the concentration of BaX2 in the reactant mother liquor and the control of the adding rate of a reactant solution comprising an aqueous solution of an inorganic fluoride.
The present invention is as follows:
 less than 1 greater than  A rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor which is represented by the basic compositional formula (I):
xe2x80x83Ba1xe2x88x92xMIIxFX:yMI,zLnxe2x80x83xe2x80x83(I)
wherein MII represents at least one alkaline earth metal selected from the group consisting of Sr and Ca; MI represents at least one alkaline metal selected from the group consisting of Li, Na, K, Rb, and Cs; X represents at least one halogen selected from the group consisting of Cl, Br, and I; Ln represents at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm, and Yb; and x, y, and z represent, respectively, numerals within the ranges of 0xe2x89xa6xxe2x89xa60.5, 0xe2x89xa6yxe2x89xa60.05, and 0 less than zxe2x89xa60.2, and
which has a grain size median diameter (Dm) of 1 to 10 xcexcm,
"sgr"/Dm of 50% or less where "sgr" is a standard deviation of grain size distribution, and
a grain aspect ratio within the range of from 1.0 to 2.0.
 less than 2 greater than  The rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , wherein the grain shape is tetradecahedral.
 less than 3 greater than  The rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , wherein Ln in the basic compositional formula (I) is Ce or Eu.
 less than 4 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing BaX2, a water-soluble compound of Ln, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0, wherein the solution has a BaX2 concentration of 2.5 mol/L or less if X is Cl or Br, or alternatively, a BaX2 concentration of 5.0 mol/L or less if X is I after the foregoing components are dissolved;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding an aqueous solution of an inorganic fluoride salt to the reactant mother liquor kept at 20 to 100xc2x0 C. while adjusting the adding rate in such a manner that the amount of the precipitate of crystals of a phosphor precursor to be formed during the addition is within the range of from 0.001 to 10 N/minute, where N is the amount of the precipitate of crystals of a phosphor precursor to be finally obtained;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof.
 less than 5 greater than  The process of  less than 4 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the inorganic fluoride salt is ammonium fluoride or a fluoride of an alkaline metal.
 less than 6 greater than  The process of  less than 4 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein a precision cylinder pump is used for the addition of the aqueous solution of an inorganic fluoride in the precipitate forming step.
 less than 7 greater than  The process of  less than 4 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the adding rate of the aqueous solution of an inorganic fluoride in the precipitate forming step is adjusted to 0.01 to 1.0 N/minute.
 less than 8 greater than  The process of  less than 4 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the adding rate of the aqueous solution of an inorganic fluoride in the precipitate forming step is constant, or alternatively, varies continuously or discontinuously with respect to addition time.
 less than 9 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing BaX2, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0 (excluding, however, any of the above components which is to be added simultaneously with an aqueous solution of an inorganic fluoride salt to thereby cause no deficiency thereof), wherein the solution has a BaX2 concentration of 2.5 mol/L or less if X is Cl or Br, or alternatively, a BaX2 concentration of 5.0 mol/L or less if X is I after the foregoing components are dissolved;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding an aqueous solution of an inorganic fluoride salt, an aqueous solution containing a water-soluble compound of Ln, and an aqueous solution of a halide, nitrate, nitrite, or acetate of MI and/or an aqueous solution of a halide, nitrate, nitrite, or acetate of MII simultaneously to the reactant mother liquor which has been kept at 20 to 100xc2x0 C.;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof.
 less than 10 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing BaX2, a water-soluble compound of Ln, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0 (excluding, however, any of the above components which is to be added simultaneously with an aqueous solution of an inorganic fluoride salt to thereby cause no deficiency thereof), wherein the solution has a BaX2 concentration of 2.5 mol/L or less if X is Cl or Br, or alternatively, a BaX2 concentration of 5.0 mol/L or less if X is I after the foregoing components are dissolved;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding an aqueous solution of an inorganic fluoride salt, an aqueous solution containing a water-soluble compound of Ln, and an aqueous solution of a halide, nitrate, nitrite, or acetate of MI and/or an aqueous solution of a halide, nitrate, nitrite, or acetate of MII (excluding the case where both x and y of the basic compositional formula (I) are 0) simultaneously to the reactant mother liquor which has been kept at 20 to 100xc2x0 C.;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof.
 less than 11 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing NH4X, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0 (excluding, however, any of the above components which is to be added simultaneously with an aqueous solution of an inorganic fluoride salt to thereby cause no deficiency thereof), wherein the solution has an NH4X concentration of 4.5 mol/L or less after the foregoing components are dissolved;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding an aqueous solution of BaX2, an aqueous solution of an inorganic fluoride salt, an aqueous solution containing a water-soluble compound of Ln, and an aqueous solution of a halide, nitrate, nitrite, or acetate of MI and/or an aqueous solution of a halide, nitrate, nitrite, or acetate of MII, simultaneously and in such a manner that the molar ratio of fluorine in the inorganic fluoride to BaX2 is kept constant, to the reactant mother liquor which has been kept at 20 to 100xc2x0 C.;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof.
 less than 12 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing NH4X, a water-soluble compound of Ln, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0 (excluding, however, any of the above components which is to be added simultaneously with an aqueous solution of an inorganic fluoride salt to thereby cause no deficiency thereof), wherein the solution has an NH4X concentration of 4.5 mol/L or less after the foregoing components are dissolved;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding an aqueous solution of BaX2, an aqueous solution of an inorganic fluoride salt, an aqueous solution containing a water-soluble compound of Ln, and an aqueous solution of a halide, nitrate, nitrite, or acetate of MI and/or an aqueous solution of a halide, nitrate, nitrite, or acetate of MII (excluding the case where both x and y of the basic compositional formula (I) are 0), simultaneously and in such a manner that the molar ratio of fluorine in the inorganic fluoride to BaX2 is kept constant, to the reactant mother liquor which has been kept at 20 to 100xc2x0 C.;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof.
 less than 13 greater than  The process of  less than 9 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein, in the precipitate forming step, the aqueous solution of an inorganic fluoride salt is added by adjusting the adding rate thereof in such a manner that the amount of the precipitate of crystals of a phosphor precursor to be formed during the addition is within the range of from 0.001 to 10 N/minute, where N is the amount of the precipitate of crystals of a phosphor precursor to be finally obtained.
 less than 14 greater than  The process of  less than 11 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein, in the precipitate forming step, the aqueous solution of an inorganic fluoride salt and the aqueous solution of BaX2 are added by adjusting the adding rates thereof in such a manner that the amount of the precipitate of crystals of a phosphor precursor to be formed during the addition is within the range of from 0.001 to 10 N/minute, where N is the amount of the precipitate of crystals of a phosphor precursor to be finally obtained.
 less than 15 greater than  The process of  less than 9 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the inorganic fluoride salt is ammonium fluoride or a fluoride of an alkaline metal.
 less than 16 greater than  The process of  less than 9 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the adding rates of the aqueous solutions, which are to be added simultaneously with the aqueous solution of an inorganic fluoride salt and which are other than the solution of an inorganic fluoride salt and the aqueous solution of BaX2, vary continuously or discontinuously during the addition time in the precipitate forming step.
 less than 17 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing NH4X, a water-soluble compound of Ln, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0, wherein the solution has an NH4X concentration of between 2.0 and 4.5 mol/L;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding an aqueous solution of an inorganic fluoride salt and an aqueous solution of BaX2, in such a manner that the molar ratio of fluorine in the inorganic fluoride salt to BaX2 is kept constant, to the reactant mother liquor which has been kept at 20 to 100xc2x0 C.;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof;
characterized in that, in the precipitate forming step, the average adding rates of the aqueous solution of an inorganic fluoride salt and the aqueous solution of BaX2 in the period ranging from the start of the addition to t (0 less than t less than T, where T indicates the time when the addition ends) are faster than the average adding rates, respectively, in the period ranging from t to T.
 less than 18 greater than  The process of  less than 17 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the precipitate forming step consists of a first precipitate forming step and a second precipitate forming step.
 less than 19 greater than  The process of  less than 18 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein N and N1 satisfy the following relational formula where N is the amount of the precipitate of crystals of a phosphor precursor to be finally obtained and N1 is the amount of the crystals of a phosphor precursor to be precipitated in the first precipitate forming step.
0 less than (N1/N)xe2x89xa60.8
 less than 20 greater than  The process of  less than 18 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein, in the precipitate forming step, the curve indicating the change with time of the adding rate of the aqueous solution of an inorganic fluoride salt and the aqueous solution of BaX2 has an inflection or bending point numbering n (where n represents a natural number of 1 or greater) and the first precipitate forming step is defined by the time ranging from the start of addition to the inflection or bending point if n=1, while the first precipitate forming step is defined by the time ranging from the start of addition to the midpoint between the first inflection or bending point and the second first inflection or bending point if n xe2x89xa72.
 less than 21 greater than  The process of  less than 18 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the second precipitate forming step is carried out consecutively after the first precipitate forming step, or the second precipitate forming step is carried out when a certain period of time has passed after the first precipitate forming step.
 less than 22 greater than  The process of  less than 17 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the adding rates of the aqueous solution of BaX2 and the solution of an inorganic fluoride salt are kept constant or vary continuously or discontinuously with respect to addition time in the precipitate forming step.
 less than 23 greater than  The process of  less than 17 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the inorganic fluoride salt is ammonium fluoride or a fluoride of an alkaline metal.
 less than 24 greater than  The process of  less than 17 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the adding rates of the solution of an inorganic fluoride salt and the aqueous solution of BaX2 are adjusted so that the amount of the precipitate of crystals of a phosphor precursor to be formed during the addition is within the range of from 0.001 to 10 N/minute, where N is the amount of the precipitate of crystals of a phosphor precursor to be finally obtained.
 less than 25 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing NH4X, a water-soluble compound of Ln, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0, wherein the solution has an NH4X concentration of between 2.0 and 4.5 mol/L after the foregoing components are dissolved, and for keeping the reactant mother liquor at 20 to 100xc2x0 C. while being stirred;
a crystal nuclei forming step for forming crystal nuclei of the crystals of a phosphor precursor by stirring the aqueous solution of an inorganic fluoride salt and the aqueous solution of BaX2 at a high speed while these solutions are being added and introducing the reacted suspension into the reactant mother liquor which is kept at 20 to 100xc2x0 C. and stirred;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding the aqueous solution of BaX2 and the aqueous solution of an inorganic fluoride salt, in such a manner that the molar ratio of fluorine in the inorganic fluoride salt to BaX2 is kept constant, to the reactant mother liquor which contains the suspension and is kept at 20 to 100xc2x0 C.;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof.
 less than 26 greater than  A process for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than , comprising:
a mother liquor preparing step for preparing a reactant mother liquor which is an aqueous solution containing BaX2, a water-soluble compound of Ln, a halide, nitrate, nitrite, or acetate of MII in addition if x in the basic compositional formula (I) is not 0, and a halide, nitrate, nitrite, or acetate of MI in addition if y in the basic compositional formula (I) is not 0, wherein the solution has a BaX2 concentration of 2.5 mol/L or less if X is Cl or Br, or alternatively, a BaX2 concentration of 5.0 mol/L or less if X is I after the foregoing components are dissolved, and for keeping the reactant mother liquor at 20 to 100xc2x0 C. while being stirred;
a crystal nuclei forming step for forming crystal nuclei of the crystals of a phosphor precursor by stirring the aqueous solution of an inorganic fluoride salt and the aqueous solution of BaX2 at a high speed while these solutions are being added and introducing the reacted suspension into the reactant mother liquor which is kept at 20 to 100xc2x0 C. and stirred;
a precipitate forming step for preparing the precipitate of crystals of a phosphor precursor by adding the aqueous solution of an inorganic fluoride salt to the reactant mother liquor which contains the suspension and is kept at 20 to 100xc2x0 C.;
a separating step for separating the precipitate of crystals of a phosphor precursor from the aqueous solution; and
a firing step for firing the separated precipitate of crystals of a phosphor precursor while avoiding sintering thereof.
 less than 27 greater than  The process of  less than 25 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein, in the precipitate forming step, the adding rates of the solution of an inorganic fluoride salt and the aqueous solution of BaX2 are adjusted so that the amount of the precipitate of crystals of a phosphor precursor to be formed during the addition is within the range of from 0.001 to 10 N/minute, where N is the amount of the precipitate of crystals of a phosphor precursor to be finally obtained.
 less than 28 greater than  The process of  less than 26 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein, in the precipitate forming step, the adding rate of the solution of an inorganic fluoride is adjusted so that the amount of the precipitate of crystals of a phosphor precursor to be formed during the addition is within the range of from 0.001 to 10 N/minute, where N is the amount of the precipitate of crystals of a phosphor precursor to be finally obtained.
 less than 29 greater than  The process of  less than 25 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein, in the crystal nuclei forming step, the adding rates of the solution of an inorganic fluoride salt and the aqueous solution of BaX2 are adjusted so that the amount of the crystal nuclei of a phosphor precursor to be formed in the crystal nuclei forming step is between 0 and 0.8 N, where N is the amount of the crystals of a phosphor precursor to be finally obtained in the precipitate forming step.
 less than 30 greater than  The process of  less than 25 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein the inorganic fluoride salt is ammonium fluoride or a fluoride of an alkaline metal.
 less than 31 greater than  The process of  less than 25 greater than  for preparing the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor, wherein, in the crystal nuclei forming step, the solution of an inorganic fluoride salt and the aqueous solution of BaX2 are stirred at a high speed using an instant reactor.
 less than 32 greater than  A reaction apparatus comprising:
two or more liquid adding devices for accommodating and pumping out a liquid;
an instant reactor for accommodating the liquid pumped from the two or more liquid adding devices, stirring the liquid at a high speed, and thereafter pumping out the liquid; and
a stirring tank for accommodating the liquid pumped from the two or more liquid adding devices and the liquid pumped from the instant reactor and stirring these liquids together with a reactant mother liquid which has been accommodated in the stirring tank in advance.
 less than 33 greater than  A radiographic image conversion panel having a stimulable fluorescent layer containing a stimulable phosphor, wherein the stimulable phosphor is the rare earth element-activated, alkaline earth metal fluorohalide based stimulable phosphor of  less than 1 greater than .